The invention relates generally to the field of photovoltaics. In particular, the invention relates to a method of making a layer used in a photovoltaic device and to a photovoltaic device made therefrom.
One of the main focuses in the field of photovoltaic devices is the improvement of energy conversion efficiency (from electromagnetic energy to electric energy or vice versa). Solar energy is abundant in many parts of the world year around. Unfortunately, the available solar energy is not generally used efficiently to produce electricity. Photovoltaic (“PV”) devices convert light directly into electricity. Photovoltaic devices are used in numerous applications, from small energy conversion devices for calculators and watches to large energy conversion devices for households, utilities, and satellites.
Further, the cost of conventional photovoltaic cells or solar cell, and electricity generated by these cells, is generally comparatively high. For example, a typical solar cell achieves a conversion efficiency of less than 20 percent. Moreover, solar cells typically include multiple layers formed on a substrate, and thus solar cell manufacturing typically requires a significant number of processing steps. As a result, the high number of processing steps, layers, interfaces, and complexity increase the amount of time and money required to manufacture these solar cells.
Photovoltaic devices often suffer reduced performance due to loss of light, through for example, reflection and absorption. Therefore, research in optical designs of these devices includes light collection and trapping, spectrally matched absorption and up/down light energy conversion. One of the ways to minimize the loss in a photovoltaic cell is to incorporate a wide bandgap window layer. It is well known in the art that the design and engineering of window layers should have as high a bandgap as possible to minimize absorption losses. The window layer should also be materially compatible with the absorber layer so that the interface between the absorber layer and the window layer contains negligible interface defect states. Typically, cadmium sulfide (CdS) has been used to make the window layer in photovoltaic cells, e.g. cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) solar cells. One major drawback for cadmium sulfide is its relatively low bandgap which results in current loss in the device. A thin layer of cadmium sulfide is employed in photovoltaic devices to help reduce optical loss by absorption. However, issues such as shunts between the absorber layer and the transparent conductive oxide (TCO) exist in the photovoltaic devices due to the presence of the thin cadmium sulfide layer. To overcome the above disadvantage, a high resistive transparent buffer layer is employed to prevent the shunting. In addition, the processing conditions to make some photovoltaic devices, for example devices that include cadmium telluride, are harsh, and the layers are exposed to high temperatures, therefore thermal stability of the layers at the high temperatures is an important criterion.
Therefore, there remains a need for an improved solution to the long-standing problem of inefficient and complicated solar energy conversion devices and methods of manufacture.